Modular cast iron fin tube boiler

ABSTRACT

A fluid tube boiler is disclosed wherein the heat exchanging tubes, associated headers, etc, are all cast iron. The tubes are cast with heat exchanging fins forming an integral part thereof whereby a maximum heat transfer area is provided with a minimum mass of cast iron. The various headers, manifolds, etc., which are interconnected with the tubes for distributing the fluid to the tubes are also of cast iron. The various castings are interconnected and arranged to insure an essentially uniform distribution of the fluid throughout all of the heat exchanging parts of the boiler whereby uniform circulation and heat transfer is maintained.

United States Patent [191 Fung [ 1 MODULAR CAST IRON FIN TUBE BOILER [75] Inventor: James Y. Fung, Closter, NJ.

[73] Assignee: Automation Industries, Inc., Los Angeles, Calif.

[22] Filed: Aug. 31, 1973 [21] Appl. No.: 393,399

[52] US. Cl 122/264; 122/360; 122/367 C [51] Int. Cl. F22B 15/00 [58] Field of Search 122/360, 367 R, 367 C, 122/406, 407, 264, 263, 367 A [56] References Cited UNITED STATES PATENTS 245,557 8/1881 Pond 122/235 659,623 10/1900 Mallet et a1 122/367 X 769,682 9/1904 Coppridge 122/264 1,821,683 9/1931 Whittam 122/360 2,359,816 10/1944 Wolf ct a1. 122/367 2,688,315 9/1954 Davy 122/360 2,828,723 4/1958 Miller 122/367 X June 17, 1975 Primary Examiner-Kenneth W. Sprague Attorney, Agent, or Firm-Dan R. Sadler [57] ABSTRACT A fluid tube boiler is disclosed wherein the heat exchanging tubes, associated headers, etc, are all cast iron. The tubes are cast with heat exchanging fins forming an integral part thereof whereby a maximum heat transfer area is provided with a minimum mass of cast iron. The various headers, manifolds, etc., which are interconnected with the tubes for distributing the fluid to the tubes are also of cast iron. The various castings are interconnected and arranged to insure an essentially uniform distribution of the fluid throughout all of the heat exchanging parts of the boiler whereby uniform circulation and heat transfer is maintained.

10 Claims, 14 Drawing Figures GO GO SHEET PATENTEDJUN 17 I975 SHEET Fig. 12.

MODULAR CAST IRON FIN TUBE BOILER BACKGROUND Heretofore various types of boilers have been proposed for heating various types of fluids such as water and/or for producing steam for various types of applications. In one form of fluid tube boiler, the heat exchanging core has been formed by a plurality of iron castings being stacked one upon the other so as to build up the desired thermal capacity. An example of this type of boiler is disclosed in US. Letters Pat. Nos. 2,247,796 and 3,329,933.

In another form of fluid tube boiler, various types of metal tubes have been used to form the heat exchanging core. In one type of boiler, such as disclosed in US. Pat. No. l,512,864, cast iron tubes have been employed with film cast integrally with the tube.

In other forms of boilers, sheet metal tubes have been used. A sheet metal fin has spirally wrapped around the tube to increase the surface area thereby tending to increase the rate of heat transfer. An example of this type of boiler is disclosed in US. Pat. No. 3,534,712. In a boiler of this nature, spirally wrapping the fin around the tube to increase the heat transfer area is expensive. In some designs the tubing and/or the spiral fin are made of copper because of the high thermal conductivity. However, in such designs, an expensive controlling device is needed to insure a continuous flow of water throughout all parts of the tubes and to prevent the generation of steam. A lack of water and/or the generation of steam in a tube or in some portion of the tube will allow that part of the tube to overheat. Because of the low melting point of copper, any overheating will cause the tube to burn out.

In other designs, steel tubes with spirally wrappped fins are used. Such steel tubes are excellent for very high temperatures and pressures. However, since the steel is readily susceptible to oxygen corrosion, it has not been found particularly well suited for low temperature operations.

SUMMARY The present invention provides means for overcoming the foregoing difficulties More particularly, a fluid or water tube boiler is provided wherein a plurality of cast iron tubes are employed. The tubes are made by casting iron with the heat transferring fins cast integrally thereon. The cast iron tubes are joined together by cast iron headers and manifolds to form integral heat exchanging modules. The object is to produce a heat exchanging modules. The object is to produce a heat absorption unit or module of standarized design having a predetermined number of tubes and a predetermined thermal capacity such as 500,000 B.T.U. The thermal capacity of the boiler can be increased by increments corresponding to the capacity of the individual modules used.

DRAWINGS FIG. 1 is a side view of a hot water boiler embodying one form of the present invention,

FIG. 2 is an end view of the boiler of FIG. 1,

FIG. 3 is an end view on the enlarged scale of one of the headers,

FIG. 4 is a bottom view of the header of FIG. 3,

FIG. 5 is an end view of the header,

FIG. 6 is a fragmentary front view of a portion of the header,

FIG. 7 is a fragmentary cross-sectional view of a portion of the header,

FIG. 8 is a cross-sectional view on an enlarged scale of the central portion of the cast iron finned tube structure,

FIG. 9 is a crosssectional view of the end portion of the cast iron finned tube structure and a portion of the associated header,

FIG. 10 is a cross-sectional view of a portion of the cast iron tubes,

FIG. 11 is an end view of a header embodying another embodiment of the invention,

FIG. 12 is a view of an end plate,

FIG. 13 is a view of the face of the manifold, and

FIG. 14 is a view of the opposite side of the manifold.

DESCRIPTION The boiler 10 includes a base 12 that is adapted to be mounted upon a fire proof supported 14 such as a cement pad or floor. Several inverter U-shaped channels 16 may be secured to the under side of the base 12 to maintain the base 12 in a raised spaced relation to the support 14.

The entire boiler 10 is preferably fully enclosed in a protective container 11. Normally this container is in the form of a sheet metal box having side and end panels 13 and 15 which may be readily removed for servicing, etc. These panels 13 and 15 may be provided with a considerable quantity of thermal and acoustical insulation.

A fire box or combustion chamber 18 is formed over the center portion of the base 12. This chamber 18 includes a pair of vertical side walls 20 which are positioned fairly close to the opposite edges of the base 12. These side walls 20 extend all the way from the base 12 to the top of the combustion chamber 18.

In addition the combustion chamber 18 includes a pair of end walls 22. These end walls 22 are preferably disposed directly over a pair of the channels 16 whereby a portion of the base 12 extends therebeyond. The bottoms of the end walls 22 are spaced a short distance above the base 12. This leaves openings 24 and 26 for the entrance of the combustion air. The end walls 22 also terminate a short distance below the top of the side walls 20.

It may thus be seen the side and end walls 20 and 22 form a boxlike structure having air inlet openings or vents 24 adjacent the bottom. The walls 20 and 22 are preferably fabricated from a high temperature insulating material such as a ceramic, refractory brick, etc. It is also desirable for the walls 20 and 22 to have some acoustical insulating qualities to mute the sounds of combustion.

A burner assembly 25 may be provided for burning a suitable fuel and developing the desired thermal energy. The exact nature of the burner assembly of course depends upon the nature of the fuel. However, for purposes of illustration, a gas type assembly is shown.

The burner assembly 25 is mounted inside of the combustion chamber 18 near the bottom thereof. The present burner assembly 25 includes a plurality of pipes 26 having burner jets or nozzles distributed throughout the bottom of the chamber 18 in a raised or elevated position just above the base 12 of the boiler 10. The openings 24 and 26 formed just below the end walls 22 are adequate to allow fresh air to flow into the combustion chamber 18 in adequate volume to support combustion.

A combustion control 30 may be mounted on or near the front end wall 22. The exact nature of the combustion control 30 is, of course, dependent upon the type of fuel, governmental agency requirements, the nature of the burner assembly 25, etc. However, it is effective to regulate the flow of fuel into the burner assembly 25. The overall height of the combustion chamber 18 is not believed to be particularly critical. However, the height is normally a function of the combustion rate, type of burner used, etc.

A heat exchanger core 32 is provided at the top of the combustion chamber 18 so as to absorb heat from the products of combustion. In the present instance this core 32 is of the so-called water tube variety whereby the water passes through the core 32 and is heated. This core 32 is effective to insure that the water circulating three-through is maintained in intimate heat exchanging relationship with the hot gases as they flow vertically upward from te combustion chamber 18 and produces a highly efficient heat transfer.

A hood or flue collector 34 may be disposed across the top of the combustion chamber 18 immediately over the heat exchanger core 32. This is effective to collect the expended product of combustion and direct them into a exhaust duct or smoke stack. As will become apparent, the height of this boiler is very small. As a consequence, it is feasible to build the flue collector 34, exhaust duct, etc., as an integral part of the sheet metal box containing the boiler 10.

The heat exchanger core 32 may be fabricated in any desired manner. However, in the present instance it is composed of a series of heat absorbing units or modules 36 of a standarized design. The modules 36 are all substantially identical to each other. Each module 36 is adapted to produce some predetermined increment of energy. For example each module 36 may have a thermal capacity such as 500,000 B.T.U. By adding additional modules to the boiler the thermal capacity of the boiler may be built up to any desired level.

For illustrative purposes, in the present embodiment only two modules 36 are illustrated. However, it should be understood any desired number of modules 36 may be used to build-up a heat exchanger core 32 having the desired thermal capacity.

Each of the individual modules 36 includes a pair of headers 38 with a group or bundle of cast iron, finned tubes 40 extending between the two headers 38. The headers 38 are adapted to be disposed adjacent the opposite ends of the combustion chamber 18 and may be mounted upon or adjacent to the end walls 22.

The headers 38 are preferably all identical to each other. The headers 38 are preferably cast in two separate parts. The first part is hollow and forms the main body 42 of the header. The top and bottom sides 44 and 46 of this body 42 are substantially horizontal. For reasons which will become apparent subsequently the two ends 48 and 50 are preferably slightly inclined to the vertical. This will facilitate mating with the ends of the adjacent headers 38 when more than one module 36 is employed. The body 42 also includes a front or face 52 which is substantially vertical. This face 52 includes a separate opening for each of the individual tubes.

Each of the headers 38 includes an enlarged riser 54 which opens through one side 46 of the header 38. This riser 54 is effective to allow water to enter or leave the header 38.

The rear of the body 42 is open. However, it is closed and sealed by a cast iron cover 56. The edges of the cover 56 and/or the body 42 includes a recess or groove for receiving a gasket. This gasket is effective to seal the mating between the backside of the main body 42 and the front of the cover 56. This is effective to enclose and seal the interior of the header 38. The cover 56 may be secured in position by a series of bolts 58 around the periphery thereof. In addition, one or more tie rods may extend from one cover to the cover on the opposite end of the boiler 10. Such a tie rod 60 compresses all of the components together against the expansive forces of the water pressure and the thermal expansion and contraction in heating. However, it has been found desirable for the tie rod 60 (FIG. 9) to only extend the length of the tube 66 whereby the tube 66 is axially compressed. Such an internal tie reduces the problem of thermal expansion and corrosion of the tie rod.

It is frequently desirable to apply an internal coating to the inside surfaces of the castings including the tubes. The ability to visually inspect the interior of the headers 38 and tubes 40 will permit confirmation that such a coating is of a high quality and free from any voids or discontinuities. If the coating is not complete and/or has openings therein, the boiler 10 may fail prematurely because of corrosion, etc. In addition, by being able to remove the back cover 56 from the header 36, it is possible to inspect the boiler after it has been in service and to remove any lime deposits, etc., which may have accumulated in the tubes.

Each module 36 includes a bundle or group of tubes 40. The number of tubes 40 which are employed in a module 36 may be selected to produce the desired heat transfer. By way of example in the present instance each of the modules 36 includes six separate tubes 40 to provide a total thermal capacity of about 500,000 B.T.U. per module 36.

The individual tubes 40 are cast from iron by essentially conventional techniques. The tubular section includes a cylindrical passage 64 of essentially uniform diameter which extends the entire length of the section 68.

In addition, a series of radial fins 62 are cast integrally on the outside of the tube section 68. The fins 62 are preferably uniformly spaced from each other and of uniform thickness. The exact dimensions of the fins 62, their spacing, etc., are selected to provide an optimum heat transfer ratio.

The tubes 40 are preferably cast in one continuous length. However, under some circumstances, (for example limitations in the casting process) it has been found necessary to cast the tubes 40 in shorter sections 68 and to then join these sections 68 end-to-end to make up a tube of the full desired length.

The interiors of the mating ends of the tube sections 68 are machined to provide a smooth slightly tapered surface suitable for use with a push nipple 70. The ends of the sections 68 are then forced together to make up a tube 40 of the desired length.

The outer ends of the tubes 40 are machined to fit into openings 72 in the front of header 38. This interconnection may be in the form of a press fit as illustrated. However, it should be understood that any type of a fitting such as a push nipple, etc., may be used to join the sections to each other and to join the tubes 40 to the openings 72 in the headers 38.

In the present instance the cast iron finned tubes 40 are arranged in two separate levels or tiers, i.e., an upper layer 74 and a lower layer 76. It can be appreciated that the tubes 40 may be arranged in as many tiers as desired. However, it has been found that if more two tiers are used, the tubes in the upper tiers are somewhat less efficient. First of all, they are at least partially shielded from the combustion process. For example, the upper tubes are in the shadows of the tubes in the lower levels. As a consequence, upper tubes are not directly exposed to any significant amount of the radiant energy from the combustion process.

Also, as the number of tiers increase the resistance to the flow or passage of the hot gases and the temperature of the gases decreases. Because of these and other factors, increasing the number of tiers beyond two tends to be a situation of diminishing returns.

As may best be seen in FIGS. 6 and 10, the cast iron, finned tubes 40 in the two layers 74 and 76 are staggered from each other. More particularly, the tube in the upper layer 74 is directly aligned above the space 78 between the lower tubes 40. This exposes at least a portion of the upper tube to the radiant energy present in the combustion process. Also, the hot combustion gas must flow vertically upwardly through the restricted space between the lower tubes and against the bottom of the upper tube. This insures a turbulent flow whereby the hot gases always contact the tubes.

In addition, as shown in FIG. 10, a plurality of tube baffles 75 may be provided. These baffles 75 are folded such that they extend downwardly between the adjacent upper tubes. The baffles 75 include extensions or wings 77 extending over the tops of the tubes. The adjacent edges of the wings 77 are slightly separated from each other to form a restricted vent 79. In addition, the wings 77 fit closely to the edges of the fins 62 so as to direct the hot exhaust gases directly onto the tubes and fins. This is effective to improve the heat transfer rate and efficiency of the boiler.

As indicated before, any desired number of modules 36 may be employed to build-up the required thermal capacity. If as in the present instance, more than one module 36 is desired, the additional modules are installed at the top of the combustion chamber 18 with the various headers 38 joined end-to-end. This provides a continuous double layer of tubes 40 across the entire width of the boiler 10. since the tubes 40 in the two layers 74 and 76 are staggered the ends 48 and 50 of the headers 38 are also inclined. However, the inclined ends 48 and 50 of the headers 38 will mate and fit together correctly.

A tubular cast iron manifold 80 and 82 is provided on each end of the boiler for supplying water to the headers 38 and/or collecting the water discharged from the headers 38. Each manifold 80 and 82 has an enlarged cylindrical section 84 which is approximately the same length as the combined widths of the two headers 38. Each manifold 80 and 82 includes separate risers 84 which mate with the risers 54 on each header 38.

One end of the manifold 80 or 82 is normally closed by means of a suitable cap or closure plate 86. The other end of the manifold includes a flanged fitting 88 for being connected to one of the water pipes in the heating system.

It can be seen from the drawings and particulary FIG. 1 that the header 38 and the manifold on one end of the boiler 10 are inverted from the header 38 and the manifold 82 on the opposite ends of the boiler 10. This permits all of the manifolds 80 and 82 being identical to each other and all of the headers 38 being identical to each other or else being of the opposite hand, i.e., mirror images. This of course allows a reduction in the number of parts, etc., which may be required.

In addition, this facilitates the flow of water and in particular maintaining a uniform distribution of the water circulating through all of the tubes. During normal operation the return water from the heating system enters the lower manifold 80 and flows horizontally there-along. This water divides equally between the two risers 84 and then flows upwardly into the headers 38. If there is a high rate of flow, the water entering the manifold may have large amounts of kinetic energy as it enters the manifold 80 and develops a high pressure when it reaches the far end of the manifold. Because of this effect, care must be taken to proportion the disposition and dimensions of the manifold 80, risers 84 and 54, etc., to produce an equal division flow of the water.

When the water circulates up through the riser 54 and into the interior of the header 38 is then divides and enters the various tubes 40 to flow to the opposite header 38. The arrangement of the riser 54, the size, etc., of the interior of the header should be proportioned to insure an equal division of the water between the tubes 40. When the water exits from the tubes 40 it flows into header 38 and then into the manifold 82. The water leaves the manifold 82 from the end opposite to the end where it enters the manifold 80. As a consequence, the distance the water travels is always the same irrespective of which tube 40 it passes through. It can be appreciated this insures a uniform distribution of the flow of the water throughout all of the parts of the heat exchanging core.

As an alternative, the embodiment shown in FIGS. 11 through 14 may be used. The boiler of this embodiment is substantially identical to the boiler of the first embodiment except for the modules and particularly the headers 102 thereof.

The headers 102 are adapted to be mounted above the walls 22 in essentially the same manner as the headers 38. This will insure the cast iron tubes 32 extending across the top of the combustion chamber 18. The two headers 102 are essentially identical to each other whereby they can merely be inverted when they are in stalled. Each of the headers 102 includes a tube sheet or end plate 104 and a manifold 106.

The end plate 104 is an essentially flat member of uniform thickness. The top and bottom edges 108 and 110 of the end plates 104 are normally substantially straight and adapted to be disposed in substantially straight and adapted to be disposed in substantially horizontal planes.

Each of the end plates 104 has openings 112 therethrough. These openings 112 are adapted to receive the ends of the finned tubes 32 and accordingly they may be positioned to conform to the arrangement of the individual tubes within the bundle.

As may best be seen in FIG. 12, the holes or openings 112 are arranged in two separate rows 114 and 116 to thereby provide two tiers of tubes 32. In addition, the

holes 112 in the two rows 114 and 116 are staggered laterally whereby the finned tubes 32 are displaced essentially the same as in FIG. 10.

The ends of the tubes 32 may be secured in the openings 112 through the end plate 104 by any convenient means. For example, the outside of the end of the tube 32 may be machined so as to be some sort of press fit into the openings 112. In addition, a gasket may be provided to further seal the junction. Alternatively, the inside of the tube may be machined to receive some sort of a push nipple.

It may be appreciated that when all of the tubes 32 in the bundle have their opposite ends securely anchored in the openings 113 through the plates 104, a rigid structure is formed. This can be handled as an integral structure.

The opposite ends 120 and 122 of each end plate 104 are notched or otherwise off-set. This allows the end 120 of one plate to abut against the end 122 of the adjacent plate while maintaining the desired lateral spacing of the tubes 32 in the two tiers. It will thus be seen these off-set ends 120 and 122 serve the same function as the slopping ends 48 and 50 in the first embodiment.

The mating surfaces of the off-set ends 120 and 122 may be slightly beveled so as to improve the mating and sealing between the plates. In addition, it is desirable to provide an end plug or section 124 to close and seal the openings which would otherwise be left at the ends of the modules.

The manifold 106 is preferably cast as a single piece. In this embodiment it includes a tubular segment 128 having a cylindrical passage 130 therethrough. This has an enlarged diameter corresponding to the intake pipe and the outlet pipe.

The tubular segment 128 in essence acts as a main for supplying water to its respective module or for receiving the water discharged from the module. The opposite ends of the segment 128 have enlarged flanges 132 extending radially outwardly. The faces of these flanges 132 are adapted to mate with the faces of the flanges 132 on an adjacent manifold 106 if multiple modules are used, the intake outlet pipe and/or a closure plate. It will thus be seen the water can flow laterally straight across the end of the boiler to or from the outlet or inlet pipes.

The manifold 106 includes one or more branch or feeder passages 134. This passage 134 extends laterally from the main passage 130 and opens into an enlarged distribution chamber 136. The chamber 136 is surrounded by a flange 138 which forms a face 140 on the side of the manifold 106. This face 140 is adapted to mate with the periphery of the end plate 104. A plurality of bolt holes are provided whereby the manifold 106 is bolted on to the end plate 104. The enlarged chamber 136 will thereby communicate directly with the interior of the finned tubes 32. An annular recess 142 may be provided in the face 140 of the manifold 106 and/or the end plate to seal the enlarged chamber 136.

The ends of the flange 138 are staggered or offset similar to the ends 120 and 122 of the end plates 104. However, it has been found desirable to provide a limited amount of clearance space between the adjacent ends. This allows a certain amount of freedom in positioning the manifolds 106 on the end plates 104 without mechanical interference, etc. A resilient gasket 144 may be provided between the two flanged ends of the two tubular sections 128. This gasket 144 is preferably sufficiently resilient to allow a limited mount ofworking, etc., as a result of thermal expansion and contraction, misalignment, etc.

The dimensions of the passages and 134 and the enlarged chamber 136 are arranged to insure a uniform flow of the water into and through the various cast iron tubes 32.

What is claimed is:

1. The combination of a combustion chamber,

a cast iron header disposed at each end of the combustion chamber,

a plurality of openings in said headers aligned with each other,

a bundle of case iron, finned tubes disposed in the combustion chamber and extending across said combustion chamber, the opposite ends of the tubes in said bundle being disposed in said aligned openings and communicating with the headers,

the opposite ends of said tubes and said openings being tapered to form a compression seal therebetween.

a tie rod disposed inside of at least one of the tubes, said tie rod extending the full length of the tube and creating a force which compresses the headers onto the tubes and the seal between the ends of the tubes and the openings,

manifolds on the opposite ends of said combustion chamber, each of said manifolds being interconnected with the header on the respective end of the combustion chamber, and

a flue collector disposed above the tubes and enclosing the top of the combustion chamber.

2. The combination of claim 1 wherein said headers include a main body having a sidewall and an open backside,

said sidewall including said plurality of openings, and

a cover disposed over said backside and enclosing said header, said cover being removable to provide an access into the interiors of said headers and said tubes.

3. The combination of claim 2 wherein the headers and said bundle of tubes form a module,

said openings are disposed in two staggered, horizontal rows,

the cast iron, finned tubes in said bundle are staggered according to said openings and are disposed in two layers, and

the ends of said header are contoured according to said stagger and are adapted to mate with the ends of said headers in adjacent modules.

4. In a boiler having a firebox, combustion means in said firebox and a flue collector for collecting the gases 5 from the combustion means, a plurality of heat absorbing modules, each of said modules being identical to the other modules and including a first cast iron header adapted to be disposed on one side of said firebox, a second cast iron header adapted to be disposed on the other side of said firebox, each of said headers being substantially identical to the other header and having the opposite ends thereof contoured to mate with the end of the header in an adjacent module, a plurality of tapered openings in each of said headers,

a plurality of cast iron tubes, the opposite ends of said tubes being tapered to fit into said headers to thereby be rigidly interconnected with said headers whereby said module is a rigid self-contained structure. said tubes extending from one header to the other header whereby said tubes will extend across the firebox and over said combustion means, and

a plurality of cast iron fins on each of said tubes, said fins being cast integral with the tubes.

5. The module of claim 4 wherein each of said headers include an end plate having openings therein to receive the ends of said cast iron tubes, and

a manifold removably secured to said end plate, said manifold when secured to said end plate being effective to form an enlarged chamber communicating with said tubes, said manifold when removed from said end plate being effective to form an access opening into said headers and said tubes.

6. The module of claim 4 wherein each of said headers include a manifold having a face on one side and an enlarged chamber therein,

a plurality of openings in said face communicating with said chamber and adapted to receive the ends of said tubes. and

a removable cover adapted to be removably secured to said manifold. said cover when secured to said manifold being effective to seal said chamber and when removed from said manifold being effective to provide access to said tubes.

7. A heat absorbing module for use in a boiler having a combustion chamber and a plurality of heat absorbing modules in said combustion chamber identical to each other, each of said modules including a pair of end plates adapted to be disposed on the opposite sides of the firebox,

a plurality of openings through said end plates, said openings being tapered,

a bundle of cast iron water tubes having fins cast integral therewith, each of said tubes having its opposite ends tapered to mate with said openings, said tapered ends being forced into said tapered openings and rigidly connected to said sheets whereby the module is a rigid self-contained structure, said tubes being positioned between the two end plates so as to extend across said firebox above said combustion means when said module is properly disposed in position in said boiler, and

a manifold removably secured on each of said end plates, said manifold when secured to said end plates being effective to form enlarged chambers communicating with said tubes and when removed from said end plates being effective to form access openings into said tubes.

8. The module of claim 7 wherein the openings in said end plates are in two separate rows and laterally displaced from each other whereby said tubes are arranged in two tiers, and

the opposite ends of said end plates are shaped to conform to the lateral displacement of the staggered tubes and to mate with the opposite ends of the end plates in adjacent modules.

9. The module of claim 8 including a tie rod disposed inside of at least one of said tubes and effective to impose a compressive load on the end plates which forces the parts of the module together.

10. The module of claim 8 wherein the ends of said tubes and the openings in the end plates are tapered to form a push fit therebetween. 

1. The combination of a combustion chamber, a cast iron header disposed at each end of the combustion chamber, a plurality of openings in said headers aligned with each other, a bundle of case iron, finned tubes disposed in the combustion chamber and extending across said combustion chamber, the opposite ends of the tubes in said bundle being disposed in said aligned openings and communicating with the headers, the opposite ends of said tubes and said openings being tapered to form a compression seal therebetween. a tie rod disposed inside of at least one of the tubes, said tie rod extending the full length of the tube and creating a force which compresses the headers onto the tubes and the seal between the ends of the tubes and the openings, manifolds on the opposite ends of said combustion chamber, each of said manifolds being interconnected with the header on the respective end of the combustion chamber, and a flue collector disposed above the tubes and enclosing the top of the combustion chamber.
 2. The combination of claim 1 wherein said headers include a main body having a sidewall and an open backside, said sidewall including said plurality of openings, and a cover disposed over said backside and enclosing said header, said cover being removable to provide an access into the interiors of said headers and said tubes.
 3. The combination of claim 2 wherein the headers and said bundle of tubes form a module, said openings are disposed in two staggered, horizontal rows, the cast iron, finned tubes in said bundle are staggered according to said openings and are disposed in two layers, and the ends of said header are contoured according to said stagger and are adapted to mate with the ends of said headers in adjacent modules.
 4. In a boiler having a firebox, combustion means in said firebox and a flue collector for collecting the gases from the combustion means, a plurality of heat absorbing modules, each of said modules being identical to the other modules and including a first cast iron header adapted to be disposed on one side of said firebox, a second cast iron header adapted to be disposed on the other side of said firebox, each of said headers being substantially identical to the other header and having the opposite ends thereof contoured to mate with the end of the header in an adjacent module, a plurality of tapered openings in each of said headers, a plurality of cast iron tubes, the opposite ends of said tubes being tapered to fiT into said headers to thereby be rigidly interconnected with said headers whereby said module is a rigid self-contained structure, said tubes extending from one header to the other header whereby said tubes will extend across the firebox and over said combustion means, and a plurality of cast iron fins on each of said tubes, said fins being cast integral with the tubes.
 5. The module of claim 4 wherein each of said headers include an end plate having openings therein to receive the ends of said cast iron tubes, and a manifold removably secured to said end plate, said manifold when secured to said end plate being effective to form an enlarged chamber communicating with said tubes, said manifold when removed from said end plate being effective to form an access opening into said headers and said tubes.
 6. The module of claim 4 wherein each of said headers include a manifold having a face on one side and an enlarged chamber therein, a plurality of openings in said face communicating with said chamber and adapted to receive the ends of said tubes, and a removable cover adapted to be removably secured to said manifold, said cover when secured to said manifold being effective to seal said chamber and when removed from said manifold being effective to provide access to said tubes.
 7. A heat absorbing module for use in a boiler having a combustion chamber and a plurality of heat absorbing modules in said combustion chamber identical to each other, each of said modules including a pair of end plates adapted to be disposed on the opposite sides of the firebox, a plurality of openings through said end plates, said openings being tapered, a bundle of cast iron water tubes having fins cast integral therewith, each of said tubes having its opposite ends tapered to mate with said openings, said tapered ends being forced into said tapered openings and rigidly connected to said sheets whereby the module is a rigid self-contained structure, said tubes being positioned between the two end plates so as to extend across said firebox above said combustion means when said module is properly disposed in position in said boiler, and a manifold removably secured on each of said end plates, said manifold when secured to said end plates being effective to form enlarged chambers communicating with said tubes and when removed from said end plates being effective to form access openings into said tubes.
 8. The module of claim 7 wherein the openings in said end plates are in two separate rows and laterally displaced from each other whereby said tubes are arranged in two tiers, and the opposite ends of said end plates are shaped to conform to the lateral displacement of the staggered tubes and to mate with the opposite ends of the end plates in adjacent modules.
 9. The module of claim 8 including a tie rod disposed inside of at least one of said tubes and effective to impose a compressive load on the end plates which forces the parts of the module together.
 10. The module of claim 8 wherein the ends of said tubes and the openings in the end plates are tapered to form a push fit therebetween. 